Fan control system

ABSTRACT

A fan control system includes a temperature detecting circuit and a rotation rate control circuit. The detecting circuit includes a first amplifier, a second amplifier, and a thermistor. The control circuit includes a first terminal, a second terminal, and a third terminal. The detecting circuit detects temperature and outputs a voltage signal. The control circuit receives the voltage signal and controls the rotation rate of the fan according to the voltage signal.

BACKGROUND

1. Technical Field

The present disclosure relates to a control system for a fan.

2. Description of Related Art

With advancements in computer technology, greater demands have beenbeing seen on power as well as on conserving power. Fans used todissipate heat can consume a lot of power and even waste power if theyare operating faster than needed. Therefore, a precise control over fanspeed to conserve energy meanwhile ensuring proper heat dissipation isdesired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a first embodiment of a fan controlsystem.

FIG. 2 is a circuit diagram of a second embodiment of a fan controlsystem.

FIG. 3 is a circuit diagram of a third embodiment of a fan controlsystem.

FIG. 4 is a circuit diagram of a fourth embodiment of a fan controlsystem.

DETAILED DESCRIPTION

Referring to FIG. 1, a first embodiment of a fan control system forcontrolling a rotation rate of a fan 10 of an electronic device includesa temperature detecting circuit 100 and a rotation rate control circuit200.

The detecting circuit 100 is allocated to detect temperature in anenclosure housing the fan 10 of the electronic device, and convert thetemperature to a voltage signal.

The control circuit 200 includes a first terminal T1 connected to afirst power supply V-in1, a second terminal T2 connected to thedetecting circuit 100, and a third terminal T3 connected to a first endof the fan 10. A second end of the fan 10 is grounded. The controlcircuit 200 receives the voltage signal from the detecting circuit 100,and controls the rotation rate of the fan 10 according to the voltagesignal.

The detecting circuit 100 includes a first amplifier U1, a secondamplifier U2, a thermistor RT, and resistors R1˜R4. The thermistor RT isa negative temperature coefficient thermistor.

A non-inverting input of the first amplifier U1 is connected to a secondpower supply V-in2 via the resistor R1. An inverting input of the firstamplifier U1 is grounded via the resistor R2. An output of the firstamplifier U1 is connected to the non-inverting input of the firstamplifier U1 via the resistor R3. The output of the first amplifier U1is also connected to a non-inverting input of the second amplifier U2via the thermistor RT. An inverting input of the second amplifier U2 isgrounded. An output of the second amplifier U2 is connected to thenon-inverting input of the second amplifier U2 via the resistor R4.

Power terminals of the first amplifier U1 and the second amplifier U2are connected to the first power supply V-in1. Ground terminals of thefirst amplifier U1 and the second amplifier U2 are grounded.

The control circuit 200 includes a third amplifier U3, a metal oxidesemiconductor field effect transistor (MOSFET) Q1, and resistors R5 andR6.

A drain of the MOSFET Q1 functions as the first terminal T1 of thecontrol circuit 200. A source of the MOSFET Q1 functions as the thirdterminal T3 of the control circuit 200, and is also grounded via theresistors R5 and R6 in series. A non-inverting input of the thirdamplifier U3 functions as the second terminal T2 of the control circuit200, to connect to the output of the second amplifier U2 of thedetecting circuit 100. A node between the resistors R5 and R6 is labeled“A”. An inverting input of the third amplifier U3 is connected to thenode A. An output of the third amplifier U3 is connected to a gate ofthe MOSFET Q1. A power terminal of the third amplifier U3 is connectedto the first power supply V-in1. A ground terminal of the thirdamplifier U3 is grounded.

The first amplifier U1 and the resistor R3 compose a deep negativefeedback circuit. The first amplifier U1 is equivalent to an idealamplifier. A current Ii through the resistor R1 is equal to a current Iothrough the resistor R3. The relationship of a voltage Uo1 of the outputof the first amplifier U1, the current Io through the resistor R3, thecurrent Ii through the resistor R1, a voltage of the second power supplyV-in2, and resistance of the resistors R1 and R3 is shown below:Ii=V-in2/R1=Io=Uo1/R3.

The relationship of the voltage Uo1 of the output of the first amplifierU1, the voltage of the second power supply V-in2, and resistance of theresistors R1 and R3 is shown below:Uo1=V-in2×R3/R1.

The relationship of a voltage Uo2 of the output of the second amplifierU2, the voltage Uo1 of the output of the first amplifier U1, andresistance of the resistor R4 and the thermistor RT is shown below:Uo2=Uo1×R4/RT.

The relationship of the voltage Uo2 of the output of the secondamplifier U2, the voltage of the second power supply V-in2, andresistance of the resistor R1, R3, R4 and the thermistor RT is shownbelow:Uo2=V-in2×R3×R4/(R1×RT).

The resistance of the thermistor RT decreases when the temperature inthe enclosure housing the fan 10 increases. The voltage Uo2 of theoutput of the second amplifier U2 increases accordingly. The thirdamplifier U3 compares a voltage Va of the node A and the voltage Uo2 ofthe output of the second amplifier U2. A voltage of the output of thethird amplifier U3 increases when the voltage Uo2 of the output of thesecond amplifier U2 increases. A voltage of the gate of the MOSFET Q1equals to the output of the third amplifier U3 and increasesaccordingly. The current of the source of the MOSFET Q1 increasesaccordingly to step up the rotation rate of the fan 10 to reduce thetemperature in the enclosure.

The resistance of the thermistor RT increases when the temperature inthe enclosure housing the fan 10 decreases. The voltage Uo2 of theoutput of the second amplifier U2 decreases accordingly. The thirdamplifier U3 compares the voltage Va of the node A and the voltage Uo2of the output of the second amplifier U2. The voltage of the output ofthird amplifier U3 decreases when the voltage Uo2 of the output of thesecond amplifier U2 decreases. The voltage of the gate of the MOSFET Q1decreases accordingly. The current of the source of the MOSFET Q1decreases accordingly to slow down the rotation rate of the fan 10.

Referring to FIG. 2, in a second embodiment of a fan control system, thethermistor RT may be interchanged with the resistor R1.

Referring to FIG. 3 and FIG. 4, in a third or fourth embodiment of a fancontrol system, the thermistor RT may be interchanged with the resistorR3 or the resistor R4 if the thermistor RT is a positive temperaturecoefficient thermistor.

The foregoing description of the exemplary embodiments of the disclosurehas been presented only for the purposes of illustration and descriptionand is not intended to be exhaustive or to limit the disclosure to theprecise forms disclosed. Many modifications and variations are possiblein light of the above everything. The embodiments were chosen anddescribed in order to explain the principles of the disclosure and theirpractical application so as to enable others of ordinary skill in theart to utilize the disclosure and various embodiments and with variousmodifications as are suited to the particular use contemplated.Alternative embodiments will become apparent to those of ordinary skillsin the art to which the present disclosure pertains without departingfrom its spirit and scope. Accordingly, the scope of the presentdisclosure is defined by the appended claims rather than the foregoingdescription and the exemplary embodiments described therein.

1. A fan control system for controlling a rotation rate of a fan,comprising: a temperature detecting circuit comprising a firstamplifier, a second amplifier, and a thermistor, wherein power terminalsof the first amplifier and the second amplifier are connected to a firstpower supply, ground terminals of the first amplifier and the secondamplifier are grounded, a non-inverting input of the first amplifier isconnected to a second power supply via a first resistor, an invertinginput of the first amplifier is grounded via a second resistor, anoutput of the first amplifier is connected to the non-inverting input ofthe first amplifier via a third resistor, the output of the firstamplifier is also connected to a non-inverting input of the secondamplifier via the thermistor, an inverting input of the second amplifieris grounded, an output of the second amplifier is connected to thenon-inverting input of the second amplifier via a fourth resistor, theoutput of the second amplifier outputs a voltage signal; and a rotationrate control circuit comprising a first terminal connected to the firstpower supply, a second terminal connected to the output of the secondamplifier to receive the voltage signal, and a third terminal connectedto the fan, to control the rotation rate of the fan according to thevoltage signal.
 2. The fan control system of claim 1, wherein thecontrol circuit comprises a third amplifier, and a metal oxidesemiconductor field effect transistor (MOSFET), a drain of the MOSFETfunctions as the first terminal of the control circuit, a source of theMOSFET functions as the third terminal of the control circuit, thesource of the MOSFET is grounded via a fifth resistor and a sixthresistor in series, a non-inverting input of the third amplifierfunctions as the second terminal of the control circuit, an invertinginput of the third amplifier is connected to a node between the fifthresistor and the sixth resistor, an output of the third amplifier isconnected to a gate of the MOSFET, a power terminal of the thirdamplifier is connected to the first power supply, a ground terminal ofthe third amplifier is grounded.